1. Field of the Invention
The present invention relates generally to fluid supply systems for vacuum pumps and, more specifically, to a cooling and lubrication system for use in association with a rotary screw vacuum pump which requires both lubrication and coolant for proper operation.
2. Description of Prior Art
Skilled artisans are familiar with many different types of vacuum pumps and systems used for providing lubrication and cooling to those pumps. For example, U.S. Pat. No. 3,556,697, which issued to Webb et al on Jan. 19, 1971, provides a sealing arrangement for a vacuum pump that has end portions of its shaft extending through end walls of the pump housing. Each end of the shaft is provided with space labyrinth seals and a conduit to conduct sealing liquid to spaces between the seals of each shaft end. Low pressure produced at both shaft end portions draws sealing liquid through the associated seals into the pump housing.
U.S. Pat. No. 3,876,345 which issued to Froede et al on Apr. 8, 1975, discloses a rotary piston combustion engine that is provided with two separate oil circulating systems. One system provides cooling oil through the piston while the other serves to lubricate the shaft and the piston bearings. Each of these systems is provided with its own oil feed pump. The pump of the lubricating system has a small delivery volume at high pressure and the pump for the cooling oil system has a large delivery volume at a low pressure.
U.S. Pat. No. 4,035,114, which issued to Sato on July 12, 1977, discloses a method for reducing power consumption in a liquid cooled rotary compressor. Liquid for cooling, lubricating and sealing are separated from each other immediately after the mixture is delivered out of a compression chamber to a delivery chamber so that gas and liquid are allowed to behave separately. This method further comprises the step of regulating the amount of liquid injected into the compression chamber when the compressor is in operation.
U.S. Pat. No. 4,173,440, which issued to Libis on Nov. 6, 1979, describes a method and a device for lubricating compressors. It provides two lubrication circuits with a main circuit for lubricating the compression chamber and the various components of the compressor when operating under load and a secondary circuit for lubricating the components on the suction side while operating under no load. This system is especially applicable for use in association with air compressors.
U.S. Pat. No. 2,937,807, which issued to Lorenz on May 24, 1960, discloses a high vacuum pump wherein a pressure differential across the pump casing at the point where a shaft passes through the casing is maintained at a small fraction of the total pressure differential between the surrounding atmosphere and the pressure maintained within the pump. This arrangement permits the shaft to rotate freely without any confinement or friction due to packing material and, therefore, permits relatively small and inexpensive motors to drive the pump impellers at high rotational speeds for prolonged periods without requiring adjustment or replacement of the packing gland.
U.S. Pat. No. 3,073,514, which issued to Bailey et al on Jan. 15, 1963, discloses a rotary compressor which includes two or more rotors disposed within an outer housing and formed with intermeshing helical glands and grooves which, in prior forms of this type of compressor, have been operated dry with the rotors not in physical contact with each other or with the housing. The compressor of this patent is capable of compressing air and other gaseous fluids efficiently to higher pressure ratios in a single stage than previously. A liquid is introduced into the compressor for the dual purpose of providing a liquid seal that closes the clearance spaces that are characteristic of a dry compressor and for directly cooling the fluid being compressed to such material extent that compression can be effected to provide usual shop air pressure in a single stage.
U.S. Pat. No. 4,394,113, which issued to Bammert on July 19, 1983, discloses a rotary screw compressor for compressing a gas. This compressor is provided with a housing that has an annular drain space surrounding the rotor shafts at a location between each shaft bearing and the working space for the purpose of removing escaping lubricant and gas. The drain space is connected through a drain passage to a closed collecting chamber which is substantially under the intake pressure of the compressor. A return passage is provided for the purpose of returning gas to at least one of the intake and the working space of the compressor and for returning lubricant to a lubrication circuit.
U.S. Pat. No. 2,470,655, which issued to Shaw on May 17, 1949, describes a cooling and lubrication system for compressors which utilizes a solution of water and water soluble oil that is prepared in suitable proportions and injected into the compression chamber for diffusion therein. It is discovered that relatively small quantities of soluble oil dispersed in an excess of water provides a solution in which the oil is disseminated sufficiently throughout the water to render the solution an efficient lubricant as well as a coolant.
U.S. Pat. No. 2,938,664 which issued to Noller on May 31, 1960, describes a pump cooling arrangement wherein the pump is cooled by a cooling medium circulated through the pump elements. This system provides the pump members with suitable cooling means, such as conduits which pass through the pump members and which have a cooling liquid or the like circulated therethrough. The pump is provided with a housing that has at least two opposite walls which define a work space therebetween. At least one working member, which has a work portion in the work space and a pair of opposite axle portions projecting through the opposite walls, is mounted for rotation relatively to the housing. The work member has a conduit extending therethrough. A temperature controlling fluid medium is circulated through the conduit means of the work member for the purpose of controlling the temperature of that work member while the same rotates in the work space relative to the housing.
In most applications, rotary screw vacuum pumps are cooled and lubricated by a common fluid which is usually a petroleum based lubricating oil. This common cooling and lubricating fluid is generally circulated in a closed system by an oil pump. In vacuum pumps of this type, the process gas being evacuated is disposed in intimate contact with the cooling and lubricating fluid. When process gas that is being evacuated contains solvents, corrosive elements or fine particulate matter, the cooling and lubricating fluid quickly becomes contaminated. The contaminated fluid would damage the bearings, gears and seals of the rotary screw vacuum pumps if a closed system with a common lubricating and cooling fluid is used under these conditions. These circumstances make the use of the rotary screw vacuum pump impractical unless some means is provided to separate the coolant from the lubricant. These separating systems are both complicated and costly. It would be beneficial to the field of vacuum pump systems if a means could be provided that would permit the use of a standard rotary screw vacuum pump in systems in which the process gas being evacuated is a "trash gas" that contains solvents, corrosives or fine particulate matter. It would be further beneficial if the standard rotary screw vacuum pump could be used in association with systems of this type without requiring internal modification. The subject invention provides such a system and permits the use of a standard rotary screw vacuum pump with a moderate amount of additional equipment.